China is the largest contributor to global atmospheric mercury (Hg), and accurate emission inventories in China are needed to reduce large gaps existing in global Hg mass balance estimates and assess Hg effects on various ecosystems. The China Atmospheric Mercury Emission (CAME) model was developed in this study using probabilistic emission factors generated from abundant on-site measurements and literature data. Using this model, total anthropogenic Hg emissions were estimated to be continuously increasing from 356 t in 2000 to 538 t in 2010 with an average annual increase rate of 4.2%. Industrial coal combustion, coal-fired power plants, nonferrous metal smelting, and cement production were identified to be the dominant Hg emission sources in China. The ten largest contributing provinces accounted for nearly 60% of the total Hg emissions in 2010. Speciated Hg emission inventory was developed over China with a grid-resolution of 36 × 36 km, providing needed emission fields for Hg transport models. In this new inventory, the sectoral Hg speciation profiles were significantly improved based on the latest data from field measurements and more detailed technology categorization. The overall uncertainties of the newly developed inventory were estimated to be in the range of -20% to +23%.

China is one of the regions with highest PM concentration in the world. In this study, we review the spatio-temporal distribution of PM mass concentration and components in China and the effect of control measures on PM concentrations. Annual averaged PM concentrations in Central-Eastern China reached over 100μgm, in some regions even over 150μgm. In 2013, only 4.1% of the cities attained the annual average standard of 35μgm. Aitken mode particles tend to dominate the total particle number concentration. Depending on the location and time of the year, new particle formation (NPF) has been observed to take place between about 10 and 60% of the days. In most locations, NPF was less frequent at high PM mass loadings. The secondary inorganic particles (i.e., sulfate, nitrate and ammonium) ranked the highest fraction among the PM species, followed by organic matters (OM), crustal species and element carbon (EC), which accounted for 6-50%, 15-51%, 5-41% and 2-12% of PM, respectively. In response to serious particulate matter pollution, China has taken aggressive steps to improve air quality in the last decade. As a result, the national emissions of primary PM, sulfur dioxide (SO), and nitrogen oxides (NO) have been decreasing since 2005, 2006, and 2011, respectively. The emission control policies implemented in the last decade could result in noticeable reduction in PM concentrations, contributing to the decreasing PM trends observed in Beijing, Shanghai, and Guangzhou. However, the control policies issued before 2010 are insufficient to improve PM air quality notably in future. An optimal mix of energy-saving and end-of-pipe control measures should be implemented, more ambitious control policies for NMVOC and NH should be enforced, and special control measures in winter should be applied. 40-70% emissions should be cut off to attain PM standard.

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As the largest coal consumer in China, the coal-fired power plants have come under increasing public concern in regard to atmospheric mercury pollution. This study developed an up-to-date and high-resolution mercury emission inventory of Chinese coal-fired power plants using a unit-based method that combined data from individual power plants, provincial coal characteristics, and industry removal efficiencies. National mercury emissions in 2015 were estimated at 73 tons, including 54 tons of elemental mercury, 18 tons of gaseous oxidized mercury and 1 ton of particle-bound mercury. Pulverized coal boilers emitted 65 tons, mainly in the coastal provinces and coal-electricity bases. Circulating fluidized bed boilers emitted 8 tons, mainly in Inner Mongolia and Shanxi Province. The average mercury emission intensity over the Chinese mainland was 18.3 g/GWh, which was similar to the limit for low-rank coal-fired units in the United States. The overall uncertainty of national mercury emission was estimated to be -19% to 20%, with the mercury content in coal being the major contributor. In most provinces, monthly mercury emissions generally peaked in December and August. However, monthly partition coefficients of southwest China were obviously lower than other regions from June to October due to the high proportion of hydropower generation.

Atmospheric ammonia (NH3) plays a crucial role in the formation of secondary inorganic aerosols (SIAs). Although China produces a large amount of NH3 emissions, it has not yet taken any measures to control NH3 emissions. Satellite retrievals show that NH3 vertical column densities (VCDs) have obviously increased in recent years, by approximately 20% from 2011 to 2014, in contrast to the decreases seen for SO2 and NO X VCDs. Evidence of the ground-based observations and satellite retrievals indicates that the increases in NH3 concentrations have weakened the benefits of the reduction in SIA concentrations (especially for nitrate) from SO2 and NO X emissions control. Results from model simulations suggest that the simultaneous control of NH3 emissions in conjunction with SO2 and NO X emissions is more effective in reducing particulate matter (PM) pollution than the process without NH3 emissions control is. Our findings indicate that the continual increases in free NH3 concentrations can result in a lower sensitivity of PM reduction to NH3 emissions control in the future, and reducing NH3 emissions is urgently required for the effective control of PM pollution in China.

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Mercury is a potent neurotoxin that poses health risks to the global population. Anthropogenic mercury emissions to the atmosphere are projected to decrease in the future due to enhanced policy efforts such as the Minamata Convention, a legally-binding international treaty entered into force in 2017. Here, we report the development of a comprehensive climate-atmosphere-land-ocean-ecosystem and exposure-risk model framework for mercury and its application to project the health effects of future atmospheric emissions. Our results show that the accumulated health effects associated with mercury exposure during 2010–2050 are $19 (95% confidence interval: 4.7–54) trillion (2020 USD) realized to 2050 (3% discount rate) for the current policy scenario. Our results suggest a substantial increase in global human health cost if emission reduction actions are delayed. This comprehensive modeling approach provides a much-needed tool to help parties to evaluate the effectiveness of Hg emission controls as required by the Minamata Convention.

Abstract. The Beijing-Tianjin-Hebei (BTH) region has been suffering from the most severe fine-particle (PM 2.5 ) pollution in China, which causes serious health damage and economic loss. Quantifying the source contributions to PM 2.5 concentrations has been a challenging task because of the complicated nonlinear relationships between PM 2.5 concentrations and emissions of multiple pollutants from multiple spatial regions and economic sectors. In this study, we use the extended response surface modeling (ERSM) technique to investigate the nonlinear response of PM 2.5 concentrations to emissions of multiple pollutants from different regions and sectors over the BTH region, based on over 1000 simulations by a chemical transport model (CTM). The ERSM-predicted PM 2.5 concentrations agree well with independent CTM simulations, with correlation coefficients larger than 0.99 and mean normalized errors less than 1 %. Using the ERSM technique, we find that, among all air pollutants, primary inorganic PM 2.5 makes the largest contribution (24-36 %) to PM 2.5 concentrations. The contribution of primary inorganic PM 2.5 emissions is especially high in heavily polluted winter and is dominated by the industry as well as residential and commercial sectors, which should be prioritized in PM 2.5 control strategies. The total contributions of all precursors (nitrogen oxides, NO x ; sulfur dioxides, SO 2 ; ammonia, NH 3 ; non-methane volatile organic compounds, NMVOCs; intermediate-volatility organic compounds, IVOCs; primary organic aerosol, POA) to PM 2.5 concentrations range between 31 and 48 %. Among these precursors, PM 2.5 concentrations are primarily sensitive to the emissions of NH 3 , NMVOC + IVOC, and POA. The sensitivities increase substantially for NH 3 and NO x and decrease slightly for POA and NMVOC + IVOC with the increase in the emission reduction ratio, which illustrates the nonlinear relationships between precursor emissions and PM 2.5 concentrations. The contributions of primary inorganic PM 2.5 emissions to PM 2.5 concentrations are dominated by local emission sources, which account for over 75 % of the total primary inorganic PM 2.5 contributions. For precursors, however, emissions from other regions could play similar roles to local emission sources in the summer and over the northern part of BTH. The source contribution features for various types of heavy-pollution episodes are distinctly different from each other and from the monthly mean results, illustrating that control strategies should be differentiated based on the major contributing sources during different types of episodes.